The increasing demand for higher data rates in cellular communications has led to the introduction of carrier aggregation as part of the 3GPP Long-Term Evolution (LTE) standard. Carrier aggregation is a technique where multiple component carriers are allocated to a user device to increase the bandwidth available for data communications, thereby increasing the data throughput for the device. The bandwidth of each of the component carriers may be between 1.4-20 MHz, and according to the LTE-Advanced (LTE-A) standard, up to five component carriers can be aggregated resulting in a maximum aggregated bandwidth of 100 MHz. In practice, most cellular service operators that support carrier aggregation aggregate two or at most three component carriers, though it is expected that more than three component carriers may be aggregated in the future if even wider bandwidths are needed or desired.
Several schemes are possible for selecting the component carriers and their bandwidths for carrier aggregation as outlined in the LTE and LTE-A standards. As shown in FIGS. 1A and 1B, in an intra-band contiguous scheme, multiple component carriers contiguous within the same operating frequency band are aggregated. In the example of FIG. 1A, two contiguous carriers, each of which has a 20 MHz bandwidth in the same operating frequency (identified as band 7), are aggregated. FIG. 1B shows a carrier aggregation scheme where three contiguous 20 MHz bandwidth carriers in the same frequency operating band (identified as band 41) are aggregated.
Intra-band carrier aggregation of contiguous component carriers is not always possible based on how cellular service operators allocate operating frequencies. When contiguous component carriers are not available, carrier aggregation may be performed using component carriers that are not contiguous in the same operating frequency band. FIG. 1C illustrates an example of intra-band non-contiguous carrier aggregation in which two component carriers from the same operating frequency band (identified as band 25) are used. The two component carriers are each of 20 MHz bandwidth, but are not contiguous because they are separated by a gap of 20 MHz.
Another carrier aggregation scheme is to aggregate component carriers from different operating frequency bands. FIG. 1D illustrates an example of inter-band non-contiguous carrier aggregation in which two non-contiguous component carriers in the same operating frequency band (identified as band 2) are aggregated with a third component carrier in a different operating frequency band (identified as band 13).
FIGS. 1E and 1F provide further examples of inter-band carrier aggregation schemes in which component carriers in different operating frequency bands are aggregated. FIG. 1E shows a two component carrier aggregation scheme in which a first component carrier in a first operating frequency band (identified as band 20) is aggregated with a second component carrier in a second operating frequency band (identified as band 8). FIG. 1F shows a three component carrier aggregation scheme in which first, second, and third component carriers, each of which is in a separate operating frequency band, are aggregated